L-Lysine is an essential amino acid, which means that it cannot be manufactured by the body and must be obtained through the diet or by supplementation. Lysine is necessary for the production of all protein in the body including hormones, enzymes, and antibodies, as well as carnitine and collagen, which is the structural protein forming all connective tissue such as skin, tendon, and bone. L-Lysine also plays a major role in calcium absorption. Some evidence suggests that L-Lysine supplementation may help to support a healthy immune system as well as proper cardiovascular function.